The batteries used in conventional home appliances or flashlights usually have plated metal end covers which form the positive and negative contact for the battery. The battery industry has used all-metallic covers on galvanic cells for many years. These covers perform three functions. First, the cover normally provides an electrical contact point for the cell. Second, the internal battery components are protected from external hazards. And third, exudate from the cell is contained within the battery. The covers are usually made of steel which has been plated with a metal such as nickel or tin. Although these covers have been used successfully in commercial products, there has always been a problem with corrosion of the covers' base steel. This type of problem is particularly noticeable when batteries have been completely discharged and then stored for an extended period of time. This situation can occur when a flashlight's batteries have been run down through continuous operation and then left in the flashlight for several months.
Conventional covers for carbon-zinc batteries have traditionally had a problem with corrosion whenever the cell's exudate was able to contact the cover or when the cell was exposed to humid conditions for a long period of time. Corrosion due to leakage is particularly noticeable after the cell has been on a long continuous discharge. The covers are usually produced by forming and punching the part from preplated steel strips. This material has micropores in the protective plate and develops stress cracks in the punching operation. When the cell's acidic electrolyte penetrates these micropores and stress cracks, corrosion of the base metal can occur. This problem detracts from the appearance of the battery and can proceed to the point that the battery will not function.